Each year, hundreds of millions of tons of inorganic solid waste, such as dust, sludges and other residues, are produced as by-products of industrial operations such as thermal power generation, incineration and other waste treatment processes, metal production and refining, and various manufacturing processes. Often, these solid wastes are considered to be hazardous or potentially hazardous to the environment, due to the presence of inorganic contaminants, such as lead, cadmium, zinc, mercury, antimony, arsenic or other environmentally sensitive contaminants, in the solid wastes.
Currently, such contaminated wastes are generally disposed of, untreated, directly into a hazardous landfill site. This method of disposal is becoming increasingly costly, and less acceptable to the public as an appropriate method for disposal of contaminated waste material. Several alternative methods of disposal have been proposed. Of these, the most advanced technologies involve immobilization of the contaminant-containing waste. Such immobilization processes generally involve encapsulating the entire mass of contaminant-containing waste in cement, lime- or silica-based materials, thermoplastics, bitumen, paraffin, polymers or glass.
Such immobilization processes actually increase the total volume of waste to be disposed of. Further, it is not possible to recover and recycle the hazardous contaminants after such an immobilization process, even though these contaminants can often be reused in other industrial processes.
While there have been several attempts to provide a method of treating these inorganic wastes whereby the contaminants are recoverable, such attempts have suffered from certain disadvantages. For example, U.S. Pat. No. 5,093,103 discloses a process for separating off volatile compounds from a mixture of solid particles comprising heating the particles in a reaction space via indirect electric heaters until the particles have a temperature of 1350.degree. C. whereby some of the volatile compounds are evaporated and the non-evaporated residue is melted. As can be expected, this process has large energy requirements, because of the necessity of forming a melt of the solid particles. Also, because of the high corrosivity of such particles at the required temperature of 1350.degree. C., any furnace to carry out this process must be made of specialty steels. Further, as the bulk of the particles have been formed into a melt, the treated particles cannot be reutilized.